Continuity mistake: During the first major battle scene, Wallace's sword has a leather looking binding around the blade at the hilt. As the battle progresses, the binding moves a third of the way down the blade and then back again.
Factual error: Throughout the film, Wallace is portrayed as a Highland clansman in traditional highland garb. This was done by Gibson to emphasise the Scottish/English conflict, but it is not historically accurate. In fact, Wallace was a Lowland knight from exactly the same ethnic background as the Anglo-Normans he was fighting and would have worn the same style of armour as they did.
Continuity mistake: When Wallace was first seen approaching the deer, he already had the bow and arrow ready, he would just need to draw back and shoot. But in a close up shot of Wallace, he was just taking out an arrow to get it ready.
Other mistake: In one of the very last scenes of the movie, when William's friend Hamish takes out William's sword to throw it as a sign of honor for William, when Hamish extends his arm back to throw the sword he only takes a step or 2, but he does not hit any of the men standing in formation directly behind him with this 5 foot long sword.
Continuity mistake: There are scenes edited out of sequence. It is just after the fight scene where Wallace and other Scots storm the fort and Wallace kills the old guy that killed his wife. Well, in that scene, Hamish's father was struck in the shoulder with an arrow, and everybody is dirty and bleeding from the fight. The very next scene we see everybody cleaned up and fine at Wallace's wife's funeral, even Hamish's father can be seen without the arrow in his shoulder. Now, the scene after that, everybody is bloody and dirty again and they are removing the arrow from Hamish's dad. The funeral was edited out of sequence.
Continuity mistake: At the end of the rock-throwing-competition scene between William and Hamish, as William is helping Hamish up there is an openly-bleeding cut on Hamish's forehead where William hit him with the small rock. Two seconds later the cut has sealed itself and there is no blood anywhere on his forehead. (00:25:40)
Continuity mistake: When Wallace is pretending to surrender after the English killed his wife, he is on a horse and he puts his hands behind his head. In all the shots from in front his hands are high on his head, in all the shots from behind his hands are low on his neck.
Audio problem: When the Scots are applying a battering ram to the city gates, you can plainly hear someone shout "Stop, drop and roll", after the English set fire to the battering ram. (01:29:35)
Continuity mistake: In the first battle scene (the first one with Wallace and the blue paint), when Wallace is charging the English you see him grabbing for his sword. In the next scene his arms are at his side. In the scene after that, he is grabbing for his sword again.
Continuity mistake: At Falkirk the order in which Longshanks, Robert the Bruce and the English soldier are standing changes from shot to shot. In some shots Bruce is between the soldier and Longshanks and in other shots the soldier is between Longshanks and Bruce without the actors ever moving.
Continuity mistake: During a scene showing Wallace and Murron hurrying up a low slope, a funny red light, possibly from a camera, briefly flashes far back in the trees behind them. Watch really carefully to spot it.
Continuity mistake: During the funeral scene for Wallace's wife we see the leader of the group of Scots that show up later in the film (after the attack on the local fort). Nobody seemed to know him but he was at the funeral with all of them...